We are using electrophysiological and computer techniques to study the mechanisms underlying transmitter release from presynaptic motor nerve terminals in vertebrates. We measure rates of quantal transmitter release by recording the amplitude and time course of transmitter-induced depolarizations of the postsynaptic skeletal muscle cell. We measure presynaptic potentials by recording intracellularly from motor nerve terminals. We want to determine the relationship between presynaptic potential changes and transmitter release in this extensively-studied preparation, specifically the time course of the influx of calcium ions associated with the action potential, and the influence of slow presynaptic afterpotentials on transmitter release.